Hasil untuk "Materials of engineering and construction. Mechanics of materials"

C. Soutis

Jiahang Chen, Zuhui Zhou, Jiaxing Guo et al.

Despite advances of single-atom catalysts (SACs) in sodium–sulfur (Na–S) batteries, their symmetric coordination geometry (e.g., M–N4) fundamentally restricts orbital-level modulation of sulfur redox kinetics. Herein, we demonstrate that hetero-diatomic Co–Y sites with Co–N4–Y–N4 coordination on N-doped carbon (Co–Y/NC) break the M–N4 symmetry constraint through d–d orbital hybridization, which is confirmed by an implementation of advanced characterizations, including the high-angle annular dark-field scanning transmission electron microscopy and x-ray absorption fine structure spectroscopy. In practical operation, the Co–Y/NC@S cathode with 61% sulfur mass fraction delivers a superior capacity (1,109 mAh/g) at 0.2 A/g, outperforming that of Co or Y SAC and further setting a new benchmark of diatomic catalysts for Na–S battery systems. Furthermore, the theoretical calculations show a hybridization-induced d-band splitting energy (ΔE = 0.5 eV), which induces electron-deficient Y sites for polysulfide adsorption (Na2S6) and electron-rich Co sites for S–S scission (barrier energy = 0.28 eV) via the d-p orbital hybridization of an asymmetric configuration. Our work establishes a strategy based on rare-earth-transition metal orbital hybridization to design asymmetric active sites for promoting multielectron sulfur redox reactions.

Wenwen Zheng, Kaichen Zhu, Sebastian Pazos et al.

When using two-dimensional (2D) materials to build electronic devices, adjacent metallic films need to be deposited to form electrodes. However, weak adhesion in high-quality van der Waals interfaces often leads to a low fabrication yield due to materials cracking and even peeling during photolithography. Several researchers use ultra-thin adhesive metallic layers, such as Ti, Cr, or Ni; while this method effectively enhances adhesion, all these metals are oxygen scavengers (in more or less degree) and they significantly alter the charge transport. Here we present a fabrication process for 2D-materials-based electronic devices that leads to high yield without the need of using adhesive metallic layers. Our method consists on using a discontinuous coverage of the 2D material during the photolithography step assisted by a negative photoresist, combined by electron beam evaporation of metal under moderate vacuum (5 × 10−6 Torr) to produce a truly van der Waals interface and avoid damaging the 2D material. When using this improved method, we systematically achieve defect-free Au/hBN interfaces with good adhesion, which lead to 100 % fabrication yield (340 devices were fabricated correctly). Electrical characterization reveals low leakage currents below 10 pA and minimal device-to-device variability, demonstrating the process’s effectiveness. Our method provides a viable pathway towards the fabrication of 2D material-based electronic devices and circuits with higher performance and reliability.

Niklas C. Fehlemann, Irene Biermann, Sebastian Münstermann

This study presents a novel framework to quantify the relationships between microstructural features and damage mechanisms in DP800 steel through high-fidelity three-dimensional sRVE simulations with novel damage indicators, which were integrated with variance-based global sensitivity analysis for the calculation of Sobol indices. The developed methodology suggests that the martensite-to-ferrite phase ratio has a stronger impact on damage tolerance than martensite strength, while the elongation of martensite is the dominant parameter for martensite fracture. For the newly introduced phase boundary decohesion indicator, the grain sizes of both phases exhibit the highest influence. A homogenized indicator for overall damage resistance and a trade-off for the two damage mechanisms further revealed the importance of phase morphology, providing insights into additional influencing factors not captured by individual mechanisms. Convergence analyses confirmed that 200–250 datapoints suffice for stable determination of the Sobol indices, confirmed by different surrogate modeling approaches. Radar chart analyses indicated that optimal microstructures for enhanced damage tolerance consist of smaller fractions of strong martensite combined with fine, spheroidal grains in both phases, aligning with established knowledge on DP steels. This approach establishes a validated basis for future optimization of microstructures and loading paths to improve damage tolerance under complex forming conditions.

Pengfei Men, Jin Di, Fengjiang Qin et al.

This paper presents an experimental and numerical investigation into the bending behaviour of reinforced concrete (RC) T-beams damaged by overheight vehicle impact strengthened with ultra-high performance concrete (UHPC). Four-point bending tests were conducted on one RC T-beam and six UHPC-strengthened RC T-beams, and the primary parameters included the length and thickness of the UHPC strengthening layer, as well as the filling area of UHPC for the damaged region. The test results demonstrated that the UHPC strengthening layer effectively delayed the development of concrete cracks, improved the bending stiffness, cracking load, and resistance of the T-beams. The UHPC-strengthened T-beams exhibited an increase in cracking and ultimate loads by 39–339 % and 26–113 %, respectively, compared to the RC T-beam. Subsequently, a finite element (FE) model of the UHPC-strengthened T-beams was developed and validated using the experimental results. A parametric study using the validated FE model was conducted, revealing that insufficient strengthened length or excessive strengthened thickness of the UHPC layer increased the risk of debonding failure. Furthermore, for T-beams experiencing bending failure, increasing the thickness and height of the UHPC layer, as well as the UHPC filling area for the damaged region, significantly improved the bending resistance, while the UHPC layer length had little effect on the bending resistance. Finally, based on the calculation theory of RC beams under bending loads and considering the strain-hardening behaviour of UHPC in tension, a design method for the bending resistance of damaged RC T-beams strengthened with UHPC was proposed and verified using the experimental and numerical results.

M. Suffo, J.F. Molina-Pérez, F. Lloret

One of the most efficient measures to prevent gamma radiation is shielding, which can take the form of protection barriers, storage containers, wall coating, bunkers, or many others aimed at minimizing the exposure of people to radiation. The materials used to this end have not changed much since the invention of X-rays, when materials with high attenuation capacity were employed, such as lead, tungsten, or concrete. These are all high-density materials and, therefore, also very heavy, and some of them are expensive and not environmentally friendly, as they do not have many possibilities with regards to their recycling. Circular economy provides an opportunity to reintroduce subproducts and waste in the same production processes that generated them or as raw matters in others. The use of sustainable materials is one of these options; however, there is little research in the field of radiation protection about the use of recycled material to this end, and there are few alternative sustainable options different from conventional materials that show similar behaviour. In our study, we have designed and built shielded panels called Mixlead® for gammagraphy, made of 100 % recyclable materials with sandwich structures combining polymeric fractions of electric cables and lead-alloy protection sheets used in the packaging of radiographic plates. With a methodology combining shielding calculations and a series of thermomechanical-radiological tests, it was possible to accurately determine the thickness of Mixlead® necessary to perform the tests with security guarantees and meeting sustainability requirements for radioactive sources of Iridium (192Ir) and Selenium (75Se), the use of the former being predominant, with an average activity of 1 GBq. In order to reduce this activity 2 and 10 times, the necessary thickness would be 24 and 79 mm respectively, which represents 3 or 4 layers of Mixlead® material.

Shuheng Zhang, Haiying Cao, Shan Xu et al.

Natural Hard Crust (NHC) with a certain thickness in the North China Plain may be used as an embankment’s bearing layer. However, the mechanical responses of pavements with NHC are not fully understood under cyclic loading. To solve this problem, an accelerated laboratory loading test on the pavements model was conducted to estimate their stress-strain-resilient modulus behaviors. This paper describes the test procedure followed and results obtained on the Soft Soil Layer (SSL) covered with NHC considering vehicle weight, vehicle speed, thickness of NHC, and Compression Modulus Ratio of NHC to SSL (CMR). The results show that vehicle weight is the precondition for the occurrence of strain hardening or strain softening in pavements with NHC. In contrast, vehicle speeds have little effect on the mechanical response of pavements. CMR and the ratio of NHC’s thickness to embankment height are the two important factors to control the plastic deformation of pavements with NHC. The accumulated responses of pavements with NHC can be described by the shakedown approach. It is desirable to consider the direct usage of NHC as a bearing layer without any foundation treatment when CMR is greater than 3.37 and the ratio of NHC’s thickness to embankment height is higher than 2. The magnitude of NHC’s load spreading effect plays an important role in the acceleration or retardation of stress dissipation in SSL layer at different stress states, which may cause the enhancement of strain hardening or strain softening effect in SSL layer.

Bo Xie, Ran Peng, Shihao Zhang et al.

Abstract Recently the alternating twisted trilayer graphene is discovered to exhibit unconventional superconductivity, which motivates us to study the electronic structures and possible correlation effects for this class of alternating twisted multilayer graphene (ATMG) systems. In this work we consider generic ATMG systems with M-L-N stacking configurations, in which the M (L) graphene layers and the L (N) layers are twisted by an angle θ (−θ). Based on analysis from a simplified k⋅p model approach, we derive generic partition rules for the low-energy electronic structures, which exhibit various band dispersions including two pairs of flat bands and flat bands co-existing with various gapless Fermionic excitations. For a mirror-symmetric ATMG system with doubled flat bands, we further find that Coulomb interactions may drive the system into a state with intertwined electric polarization and orbital magnetization orders, which can exhibit an interaction-driven orbital magnetoelectric effect.

Amrithakrishnan Bindhu, Jawahar I. Naseemabeevi, Subodh Ganesanpotti

Temperature sensors based on non-contact thermometry with better accuracy and efficiency are inevitable in various fields. In this work, a detailed study on the crystal structure and temperature dependant photophysical response of the tellurate garnet, Li3Y3Te2O12: Dy3+, is done for the first time. The crystal structure and the substitution of Dy3+ ion at the dodecahedral site of Li3Y3Te2O12 were confirmed using Rietveld refinement of the XRD patterns and Raman spectra. The characteristic sharp yellow and blue bands of Dy3+ were obtained under an excitation of 352 nm. The intense yellow band corresponding to the electric dipole transition is used to confirm the dodecahedral site occupancy of Dy3+. Moreover, an increase in the Y/B ratio (intensity of yellow to blue bands) indicates a larger degree of covalence between Dy3+ and O2− ions in the Li3Y3Te2O12 matrix. In addition, concentration quenching is caused by the exchange interaction between Dy3+ ions. Also, the decrease in decay time with higher concentrations is observed due to the enhancement in nonradiative energy transfer. The CIE coordinate of the optimum concentration is (0.39, 0.40), corresponding to the yellow region. The fluorescence intensity ratio is used to evaluate the temperature sensing properties based on the distinct fall of emission bands in the temperature range 80–300 K. A maximum relative thermal sensitivity of 1.2%/K is obtained at 80 K. These results point out that the as-prepared phosphor Li3Y3Te2O12: Dy3+ can be used as a potential candidate for ratiometric temperature sensing at low temperatures.

Yasser E. Ibrahim, Asif Hameed, Asad Ullah Qazi et al.

In the design of cold-formed steel (CFS) buildings, sheathings are used to provide lateral resistance to seismic or wind load. Many researchers have thoroughly studied the basic behavior of different sheathing (including walls sheathed with plywood, oriented strand board, gypsum wallboard, gypsum sheathing board, steel sheet sheathing, and fiberboard) with different thicknesses. However, despite many studies, the examination of existing experimental studies demonstrates that the lateral bracing and stiffness provided by the sheathing are generally ignored, and sheathing is provided as a non-structural component. This study aims at that neglected aspect. In this study, cold-formed steel shear wall (CFSSW) response has been investigated with varied thickness of hardboard sheathing used as a structural element. The main aim was to determine the contribution of sheathing in resisting lateral forces. For this purpose, three full-scale specimens (i) frame without sheathing, (ii) frame sheathed with 4 mm thick hardboard, (iii) frame sheathed with 10 mm thick hardboard were tested using a uni-directional shake table. The sheathing was screw-fastened to the cold-formed studs and tracked for the development of shear stiffness and strength in the wall system. The test results revealed that in addition to increasing the lateral stiffness of the structure, the hardboard sheathing also acts as an efficient bracing system. However, some minor but recoverable damages were also noticed. In addition, stud local buckling failure mode was observed, and it could be caused by the low anchor stiffness of using cleats instead of hold-downs. It is also important to mention that the number of tests performed in the current study was limited, and further similar research needs to be carried out before generalizing the results.

Rongxin Xiang, Lina Chen, Sheng Zhang et al.

We studied the magnetic properties of polycrystalline Y _3 Fe _5 O _12 (YIG) thin films (less than 100 nm) deposited on thermally oxidized silicon wafer by magnetron sputtering and followed by the post-annealing process. Our ferromagnetic resonance (FMR) results demonstrate that sputtering at room temperature combined with the post-annealing treatment can be an efficient method to achieve large-area (inch scale) and highly uniform YIG thin films with a low damping constant α  ∼ 7 × 10 ^−3 on cheap oxidized Si wafer. Furthermore, our spin pumping experiments demonstrate that the polycrystalline YIG/Pt system has a good spin mixing conductance, where spin current can be effectively injected into the adjacent Pt layer from YIG through the interface. Then the electrical detection of magnetic properties (e.g., spin waves) of insulating YIG film can be achieved via the inverse spin Hall effect of Pt. The electrical detection of spin waves in the large-area polycrystalline YIG/Pt on silicon wafer may help to develop new spintronic devices (e.g., magnon-based devices) by utilizing the complementary metal-oxide-semiconductor (CMOS) technology.

Ruibo Chen, Hongxia Liu, Wenqiang Song et al.

Abstract Low-voltage-triggered silicon-controlled rectifier (LVTSCR) is expected to provide an electrostatic discharge (ESD) protection for a low-voltage integrated circuit. However, it is normally vulnerable to the latch-up effect due to its extremely low holding voltage. In this paper, a novel LVTSCR embedded with an extra p-type MOSFET called EP-LVTSCR has been proposed and verified in a 28-nm CMOS technology. The proposed device possesses a lower trigger voltage of ~ 6.2 V and a significantly higher holding voltage of ~ 5.5 V with only 23% degradation of the failure current under the transmission line pulse test. It is also shown that the EP-LVTSCR operates with a lower turn-on resistance of ~ 1.8 Ω as well as a reliable leakage current of ~ 1.8 nA measured at 3.63 V, making it suitable for ESD protections in 2.5 V/3.3 V CMOS processes. Moreover, the triggering mechanism and conduction characteristics of the proposed device were explored and demonstrated with TCAD simulation.

Niloofar Sanaei, Ali Fatemi, Nam Phan

Additive manufacturing (AM) has provided an opportunity for fabricating complex parts. Fabricating these parts without defects is currently a challenge. Therefore, understanding AM defects is fundamental to the structural integrity of load carrying components, failure analysis, and defect-based modeling of mechanical performance. This work investigates defect content of metal AM specimens and correlations between defect characteristics (size, sphericity/circularity, aspect ratio) using 2D and 3D defect characterization techniques. Distributions of defect characteristics based on location throughout AM specimens were analyzed and the variabilities of defect characteristics within these specimens were studied. Laser-Based Power Bed Fusion (L-PBF) specimens manufactured with different metals, different AM machines and built directions, different surface conditions, and different thicknesses were evaluated. Significant variability in defect characteristics based on location, especially in as-built surface specimens was observed. Well-optimized process parameters and post-processing reduced the overall volume fraction of defects, and the specified variabilities, and resulted in a more random dispersion of defects around the specimens. 2D and 3D defect analysis showed similar trends regarding correlations between defect characteristics and provided complementary information about the actual defect content based on their resolution. Keywords: Additive manufacturing, Defect characterization, Computed tomography, Defect variability, Ti-6Al-4V, 17-4 PH stainless steel

LI Li-jun, MIAO Rui-xia, ZHANG Xia

Tin oxide nanowires were successful prepared using thermal evaporation method. The crystal structure and surface morphology of the nanowires were characterized by X-ray diffraction, scanning electron microscope and transmission electron microscope. The as-prepared nanowires are rutile single crystal SnO₂ structure, with diameter in 50-200nm, and length of 5-15μm, conforming to the gas-liquid-solid growth mechanism. The heater structure gas sensor was prepared using SnO₂ nanowires as the gas sensitive material. The gas sensitive performance of the samples was tested in ethanol gas concentration range of 25×10^-6-500×10^-6. The results show that the best working temperature of the sensor is about 260℃; in the 25×10^-6 and 500×10^-6 ethanol gas environment, the sensitivity is 7.54 and 111.01 respectively, response time of the sensor is 2-20s, and recovery time is 5-33s;the sensitivity and the gas concentration has a good linear relationship within the measuring range; the sensor has favourable stability with less than 5% repeated measurement error in 7 days.

A. Jung, S. Bronder, S. Diebels et al.

Open-cell metal foams are biomimetic open-porous materials mimicking the construction elements of bones. Based on their special porous microstructure, they are used as lightweight construction elements and for crash energy absorbers. Ni/Al hybrid foams are aluminium (Al) foams electrochemically coated with nanocrystalline nickel (Ni) leading to enhanced strength and energy absorption capacity. A robust understanding and knowledge of the deformation behaviour under different strain rates are essential to design crash absorbers made of foams. The present contribution is focused on the investigation of strain rate effects and is furthermore a pioneering work dealing with a full thermomechanical characterisation of the deformation behaviour in Al foams and Ni/Al hybrid foams by a combination of digital image correlation for measuring local strain fields and infrared thermography for measuring local temperature fields during the deformation process. Keywords: Open-cell metal foams, Ni/Al hybrid foams, Digital image correlation, Thermography, Deformation analysis

B. Basterra-Beroiz, R. Rommel, F. Kayser et al.

For the first time since its formulation in 1986, the theoretical approach proposed by Helmis, Heinrich and Straube (HHS model), which considers the contribution of topological restrictions from entanglements to the swelling of polymer networks, is applied to experimental data. The main aspects and key equations are reviewed and their application is illustrated for unfilled rubber compounds. The HHS model is based on real networks and gives new perspectives to the interpretation of experimental swelling data for which the entanglement contributions are usually neglected by considering phantom network models. This investigation applies a reliable constrained-chain approach through a deformation-dependent tube model for defining the elastic contribution of swollen networks, which is one of the main limitations on the applicability of classical (affine) Flory-Rehner and (non-affine) phantom models. This short communication intends to provide a baseline for the application and validation of this modern approach for a broader class of rubber materials.

Boris Vavrovič, Rastislav Menďan

In article analysis of optimal window position in external wall of different properties is provided, considering the highest surface temperature in contact area of window and its reveal.

Parviz Ghavami

Edgar Aparecido Sanches, Ademir Geraldo Cavallari Costalonga, Luana de Freitas Nascimento et al.

Corundum, sapphire or α-Al2O3 is an important technological material in many optical and electronic applications such as solid-state lasers, optical windows and, more recently, as a radiation detector. Landauer (Glenwood, IL, USA) accumulated large number of archived and stored Luxel™ dosemeters composed of Al2O3:C, which were subjected to a recovery process. Due to the importance of this advanced crystalline material in OSL dosimetry, a recovery process was developed based on the dosemeters calcination and Al2O3:C has been reused in manufacturing of new dosemeters. This paper does not aim to optimize the recovery process, but provides an opportunity to study the involved process parameters and to recover this valuable crystalline material from used dosemeters. To the best of our knowledge no other recovery process involving this dosimetric material was described in scientific literature. Fourier Transform Infrared Spectrometry (FTIR), Thermogravimetry/Differential Thermoanalysis (TG/DTA), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Optically Stimulated Luminescence (OSL) and Rietveld Refinement were used to characterize the recovered material and to check for the stability of its structural and dosimetric properties.

Toker Ömer Said, Yilmaz Mustafa Tahsin, Karaman Safa et al.

An adaptive neuro-fuzzy inference system (ANFIS) was used to accurately model the effect of gum concentration (GC) and shear rate (SR) on the apparent viscosity (h) of the ice-cream mixes stabilized with different concentrations of xanthan gum. ANFIS with different types of input membership functions (MFs) was developed. Membership function “the gauss2” generally gave the most desired results with respect to MAE, RMSE and R2 statistical performance testing tools. The ANFIS model was compared with artificial neural network (ANN) and multiple linear regression (MLR) models. The estimation by ANFIS was superior to those obtained by ANN and MLR models. The ANFIS and ANN model resulted in a good fit with the observed data, indicating that the apparent viscosity values of the ice-cream can be estimated using the ANFIS and ANN models. Comparison of the constructed models indicated that the ANFIS model exhibited better performance with high accuracy for the prediction of unmeasured values of apparent viscosity h parameter as compared to ANN although the performance of ANFIS and ANN were similar to each other. Comparison of the constructed models indicated that the ANFIS model exhibited better performance with high accuracy for the prediction of unmeasured values of apparent viscosity ɳ parameter as compared to ANN although the performance of ANFIS and ANN were similar to each other.